In the aforenoted parent application, the entire disclosure of which is incorporated herein by reference and relied upon for present disclosure purposes, there is disclosed a method of carbonating a liquid dairy product to a high level of carbonation, while not destabilizing the liquid dairy product. The process includes heating the liquid dairy product to a temperature/time range of at least 160.degree. F. for a time not in excess of 30 minutes to 200.degree. F. for a time not in excess of 5 seconds, whereby by the indigenous dairy protein, and to some extent the indigenous ash, are at least partially denatured to form a buffer thereof. The at least partially denatured liquid dairy product is then cooled to a temperature of less than about 50.degree. F. Thereafter, the cooled, denatured liquid dairy product is subjected to pressurized carbon dioxide at sufficient pressures and for a sufficient time such that the taste and mouth feel of the carbonated product is no longer that of the uncarbonated liquid dairy product, provided that at least 1.5 volumes of carbon dioxide are dissolved in the liquid dairy product during the carbonation step. The so carbonated liquid dairy product is then packaged in a closed container capable of substantially retaining the achieved degree of carbonation. The amount and extent of the heat denatured indigenous protein and ash in the dairy product is sufficient that the carbonated liquid dairy product is buffered to a pH of at least 4.0 and up to 5.7 and the carbonated liquid dairy product is highly carbonated but not destabilized.
The product which results from that process is a carbonated liquid dairy product comprising a liquid dairy product having at least partially heat denatured indigenous protein and ash therein and carbonated to at least 1.5 volumes of carbon dioxide, but wherein the amount and extent of the denatured protein and ash are sufficient that the carbonated product is buffered to a pH of at least 4.0 and up to 5.7, whereby the carbonated product is stable. The amount of carbon dioxide in the carbonated liquid dairy product is also sufficient such that the taste and mouth feel of the carbonated product is no longer that of the uncarbonated liquid dairy product.
The invention of that parent application is applicable to any liquid dairy product, including skim milk, whole milk, reduced fat content milk (e.g. 1% fat milk, 2% fat milk, etc.), cream, buttermilk, and whey, or the evaporated or condensed forms thereof, and it is particularly applicable to skim milk and whole milk, for dietary and taste reasons.
As explained in that parent application, for example, skim milk is subjected to a heat treating step where the temperature of the skim milk is raised to at least 160.degree. F. At this temperature, the indigenous milk protein will commence to denature. The rate and extent of the denaturation will depend upon the temperature to which the skim milk is raised and the time at which the skim milk dwells at that temperature. It is important that the denaturation be allowed to proceed to an extent sufficient that the partially denatured skim milk will produce a sufficient quantity of denatured indigenous protein, and to some extent denatured indigenous ash, such that the denatured protein will form an effective buffer for the carbonated skim milk. On the other hand, the denaturation must not be allowed to proceed to the extent that a denatured protein flavor becomes significantly present in the denatured skim milk. This denatured protein flavor is commonly referred to in the art as a "cooked" taste and that taste is highly objectionable.
In the latter regard, the heat treating step may be carried out at temperatures as high as about 200.degree. F. However, at this higher temperature, the allowable dwell time, i.e. without exceeding the maximum amount of denaturation which can be tolerated in order to avoid the "cooked" taste, is very short, e.g. about 5 seconds or less. Accordingly, the control of denaturation at these higher temperatures is difficult, and for this reason, it is preferred that the temperature of the heating step be no higher than 195.degree. F., since at that temperature, the time of the heating step can be up to about 15 seconds, and that amount of dwell time allows more safety in the heating step in regard to avoiding excessive denaturation and the "cooked" flavor.
Between these two times and temperatures, i.e. 160.degree. F. for no more than 30 minutes and 200.degree. F. for no more than 5 seconds, there are a variety of temperatures and dwell times which will provide sufficient denaturation to achieve the required buffering of the carbonated skim milk but which will not cause excessive denaturation and a resulting "cooked" taste to the skim milk. Specific dwell times at specific chosen temperatures, however, depend, to some extent, on uncontrolled factors. Among these factors are the particular apparatuses used for conducting the heat treating step, the specific source of the skim milk (particularly the breed of cow and the history of the handling of the skim milk), the age of the skim milk, and the rate of temperature increase during the heating step. Accordingly, the specific temperature above 160.degree. F. and below 200.degree. F. that is chosen for the heat treating step must be conducted with sufficient numbers of tests at different dwell times to ensure that the amount of denaturation does not produce a "cooked" taste in the skim milk, but on the other hand is sufficient to buffer the carbonated skim milk to a pH of at least 4.0.
After the skim milk is heat treated and denatured, it is cooled to a temperature of less than 50.degree. F. and more preferably to temperatures of about 40.degree. F. or less. At temperatures above about 50.degree. F., it is difficult to achieve the high level of carbonation required to effect the required taste and mouth feel change, due to the solubility characteristics of carbon dioxide in skim milk (or other liquid dairy products). The cooled and partially denatured skim milk is then subjected to pressurized carbon dioxide. This step may be carried out in any of the conventional beverage carbonators, e.g. those used for conventional carbonation of conventional flavored carbonated water beverages. However, irrespective of the particular apparatus being used, the pressure of the carbon dioxide used in the carbonation of the skim milk and the time for that carbonation must be such that the resulting carbonation reaches a level where the taste and mouth feel of the carbonated skim milk is no longer the taste and mouth feel of the uncarbonated skim milk. Here again, an empirical determination is quite easy to make, since when a sufficient amount of carbonation has taken place, that point can easily be detected by the taste and mouth feel change. Thus, it is only necessary to, with a series of tests, increase the degree of carbonation for any particular properly denatured liquid dairy product and taste the effect thereof. It will be quite apparent when sufficient carbonation has taken place, since at that point the taste and mouth feel will noticeably change from the taste and mouth feel of the uncarbonated skim milk.
However, it was found that for any liquid dairy product, the level of carbonation must be at least 1.5 volumes of carbon dioxide. Otherwise, for none of the liquid dairy products will the carbonation be sufficient to achieve the change in taste and mouth feel.
The products may be packaged in a very conventional manner, e.g. packaged in the manner of a conventional carbonated water beverage, e.g. packaged in pressure proof bottles and cans with conventional closures. This is an important feature of that invention and, indeed, makes the invention practical from a commercial point of view, as opposed to the processes and products of the prior art.
It is, however, preferred that the packaging take place with the carbonated skim milk being in a cooled condition, e.g. less than 50.degree. F., and more preferably less than 40.degree. F., for two reasons. First, while the present product does not experience the foaming of the prior art, it can occasion some slight degree of foaming, depending upon the particular heat treatment step, and packaging the cooled product substantially eliminates any difficulty in this regard. Secondly, since the present product is a dairy product, it must be protected from deterioration in the normal way, e.g. by refrigeration.
The carbonated skim milk should be handled in the same manner as natural skim milk. Thus, after carbonation, the carbonated skim milk should be stored, transported and handled in the same manner as any other liquid dairy product, which requires that the product always be maintained at a lower temperature. Generally speaking, therefore, the carbonated skim milk should be stored at a temperature below about 45.degree. F., e.g. refrigeration temperatures.
The carbonated skim milk, with the changed taste and mouth feel, is particularly amenable to flavoring. A flavoring may be added anytime prior to packaging of the carbonated skim milk, but it is preferred that any flavoring be added after the denaturing step, since the heat treatment of the denaturing step can adversely affect some flavors. The specification of the parent application points out that the flavors can be chosen almost as desired, with the exception that the flavors should not produce substantial acidity in the flavored carbonated skim milk, since substantial acidity could overpower the buffering system and cause destabilization of the flavored carbonated skim milk. However, within this limitation, all of the usual flavors, such as a fruit flavor, a chocolate flavor, a vanilla flavor, a soft drink flavor, or a malt flavor, may be used without difficulty. The specification of the parent application also points out that the amount of the flavor used in the carbonated skim milk may be as desired, but amounts from about 0.1% to about 3% are usual concentration ranges.